Composite pyrotechnic product with crosslinked binder and method for preparing same

ABSTRACT

A composite pyrotechnic product, especially a propellant powder for barrel weapons, containing organic energetic charges in a crosslinked binder, has a composition, expressed as weight percentages, that contains from 78% to 90% of organic energetic charges, and from 10% to 22% of an energetic crosslinked binder obtained by crosslinking, via 8% to 12% of its azide functions, a polyglycidyl azide with a number-average molecular weight of between 700 and 3000 g/mol, with a crosslinking agent containing at least two propargyl functions in its chemical formula, in the presence of a polymeric gum, chosen from polyurethane-polyester gums, polyurethane-polyether gums and mixtures thereof, the number-average molecular weight of which is greater than 20000 g/mol and the Mooney viscosity of which is between 20 and 70 ML (5+4) at 100° C.; the at least one polymeric gum representing from 1% to 5% by weight of the composition of the pyrotechnic product.

The present invention relates to composite pyrotechnic products, which are suitable especially as propellant powders for barrel weapons (more particularly for tank artillery). It concerns composite pyrotechnic products, containing a high content of energetic charges in an energetic crosslinked binder. Said products are particularly advantageous, especially in terms of force (of energetic power), of vulnerability (see below a reminder regarding this notion, which is familiar to those skilled in the art), and of field of application as regards the nature of the charges they may contain. They may conveniently be optimized in terms of erosivity.

A subject of the present invention is also a process for preparing said composite pyrotechnic products. Said process is particularly easy to perform. It does not require any solvent or any precipitation to carry out forming while the crosslinking begins, or any pre-crosslinking step.

“Homogeneous” propellant powders constituted by one or more gelatinized energetic bases having a homogeneous appearance (whence their name) are known. Among the most widely known homogeneous propellant powders, mention may be made of “smokeless” powders based on nitrocellulose alone or based on a nitrocellulose-nitroglycerine mixture. In order to improve the energy performance of these “homogeneous” powders, it is sought to incorporate therein organic (pulverulent) energetic charges. These charged powders no longer have a homogeneous appearance, but a heterogeneous appearance in which are distinguished, on the one hand, the energetic binder, and, on the other hand, the charges. Such charged powders are referred to as “composite” or “heterogeneous” powders. Such charged powders are described, for example, in French patent application FR 2 488 246.

Use of the energetic binder nitrocellulose however has the drawback of making these powders vulnerable. The term “vulnerability” refers to the property that the powders have of being able to ignite and deflagrate under the effect of an undesired, random physical phenomenon, for instance the impact of a projectile. Vulnerability is a major defect for powders intended to be transported on combat tanks. The development of modern combat machines thus led those skilled in the art to seek sparingly vulnerable propellant powders.

With this in mind, composite powders with an inert binder were proposed (constituted mainly of organic energetic charges in a synthetic resin). Such powders are markedly less vulnerable than homogeneous or composite powders with an energetic binder (nitrocellulose). However, since they contain an inert binder, these powders must, in order to deliver the necessary energy during their ignition, contain very high levels of charges, often in the region of 80% of the total weight of the powder. Composite powders with an inert binder thus have the characteristic of containing very little binder relative to their pulverulent charge. The precursor mixtures of these powders must, however, be able to be worked (in particular be able to be calendered or drawn through a die of relatively small diameter, usually comprising pins intended to create channels present in the final powder strand), and the powders must conserve their geometrical shape over time. It is particularly in reference to the production of these composite propellant powders with an inert binder for barrel weapons that those skilled in the art came up against and are still coming up against serious difficulties.

The inert binders, of synthetic origin, that may be used in the preparation of composite pyrotechnic products and that are present in their composition exist as thermoplastic binders and as thermosetting binders (thermosetting binders obtained from oligomers).

Those skilled in the art first turned toward the use of thermoplastic inert binders. Specifically, such thermoplastic binders allow, in theory, while raising temperature, mechanical working of the product to give it the desired geometry. Obviously, however, the working temperature (at which the binder is deformable) should be compatible with the stability of the charges present and, in reference to this unavoidable requirement, it is often necessary to use a solvent. The use of such a solvent complicates the implementation of the process. Patent application EP 0 036 481 describes a process for manufacturing composite explosives with a thermoplastic binder. Patent application IN 498/DEL/2001 describes a process for preparing propergol containing hexogen charges (RDX) in a thermoplastic binder. Composite products with a thermoplastic binder are generally not entirely satisfactory, since their mechanical properties are too sensitive to thermal variations.

Those skilled in the art then turned toward the use of thermosetting inert binders (obtained from oligomers), such as (crosslinkable) polyurethane binders, making it possible, after crosslinking, to constitute a three-dimensional network (in which the charges are found coated), i.e. to definitively set the geometry of the powder grain (finally obtained). The industrial scale manufacture of powders (in general composite pyrotechnic products) with a crosslinked inert binder (thus essentially constituted of a high content of charges in a minimum amount of binder) remains very difficult firstly due to the minimum cohesion and mechanical strength required for the product before crosslinking (in order to form it) and secondly due to the limited “pot life” of thermosetting resins (the term “pot life” means the period of commencement of crosslinking of the resin during which it may be worked like a plastic). Furthermore, obviously, the crosslinking temperature must be compatible with the stability of the charges and the crosslinking agent used must itself also be compatible with said charges.

Confronted with these difficulties, in the context of using thermosetting binders:

-   -   those skilled in the art proposed to work in the presence of         solvents. A solvent-based process was especially described in         French patent application FR 2 268 770. Such processes are,         however, difficult and expensive to implement, and         unsatisfactory at the industrial scale;     -   to work without solvent, with thermosetting binders, said         persons skilled in the art have widely resorted to the “casting”         or “global” technique, which consists in simultaneously mixing         in a blender the liquid elementary constituents of the resin and         the energetic charges and in casting, before polymerization, the         mixture thus obtained in a mold in order to perform the actual         polymerization therein. This technique, which has been widely         described, for example in French patent applications FR 2 109         102, FR 2 196 998, FR 2 478 623 and FR 2 491 455, may be         suitable for manufacturing composite solid propergols for rocket         or missile engines, or alternatively for manufacturing composite         explosives for device heads, which are usually used in the form         of wide-diameter products, but proves to be entirely unsuitable         for the industrial manufacture of large, medium and small         caliber composite powders and more generally for that of certain         composite pyrotechnic products;     -   for the solvent-free manufacture of composite pyrotechnic         products with a thermosetting inert binder, especially of small         diameters, said persons skilled in the art have available, at         the present time, only the following two techniques:

a) the first which consists in mixing in a blender the constituents of the resin with the energetic charges, in initiating crosslinking of the resin and, during crosslinking, in forming the product, within a very short space of time, as described, for example, in French patent applications FR 1 409 203 and FR 2 159 826. This technique requires precise control of the crosslinking kinetics in order to be able to work the paste and, as a result, it is difficult to manage at the industrial scale;

b) the second, which is much more efficient, including at the industrial scale, described in patent application EP 0 194 180. The composite pyrotechnic products obtained via this second technique are constituted mainly, on the one hand, by a polymeric binder (for example polyurethane) obtained by reaction of a polyhydroxylated prepolymer (polymer) (with a number-average molecular weight of between 2000 and 5000 and a mean functionality of hydroxyl groups (OH greater than 2 and less than 3) (PBHT, polyether or polyester, for example) with a crosslinking agent (diisocyanate), and, on the other hand, by an energetic charge, preferentially of octogen (HMX) or of hexogen (RDX), in a content of about 80% by weight. Said second technique consists:

-   -   in a first step, in mixing said polyhydroxylated prepolymer with         said energetic charge and with an amount of diisocyanate of         between 50% and 90% by weight of the stoichiometric amount         required for total polymerization (reaction) of all the hydroxyl         groups (OH) of said prepolymer and in performing the         condensation reaction of the isocyanate groups (NCO) on the         hydroxyl groups (OH) so as to obtain a partially polymerized         (crosslinked) paste;     -   in a second step, in mixing with said partially polymerized         (crosslinked) paste thus obtained the remainder of the         diisocyanate required to achieve said stoichiometric amount         required for total polymerization (crosslinking) and in         extruding the pasty mixture thus obtained; and then     -   in a third step, in completing, by hot curing, the condensation         reaction of the isocyanate groups (NCO) added during the second         step to the hydroxyl groups (OH) that are still free.

The technique under consideration thus comprises two polymerization or crosslinking steps, more precisely a first step of pre-crosslinking (or first crosslinking phase) with an amount of isocyanate that allows the production of a partially polymerized (crosslinked) paste, having mechanical strength and cohesion suitable for the implementation of the rest of the process (especially extrusion) and a second step of crosslinking leading to the final product with the desired crosslinked binder. In this, said technique overcomes the two types of difficulty mentioned above (difficulty due to the lack of mechanical strength and cohesion of the product to be extruded and problem of the “pot life”).

With reference to this second technique, it should, however, be noted that the operations for metering out the crosslinking agent (diisocyanate) to perform the pre-crosslinking are difficult. They require great precision. Moreover, the field of application of said technique is limited, in view of the nature of the crosslinking agent involved (of isocyanate type, to react with hydroxyl functions), as regards the nature of the energetic charges present, insofar as certain energetic charges (having intrinsic acidity) are capable of reacting, in a spurious reaction, with said crosslinking agent (of isocyanate type) present. The presence of such charges (EDNA, nitropyrazoles, for example) thus poses a problem for managing the complementary pre-crosslinking and crosslinking steps. Now, this presence is far from trivial, in the context of the present invention, that of composite pyrotechnic products, especially propellant powders for barrel weapons. Specifically, in this context, the use of high contents of energetic charges (see above), especially high contents of charges of RDX type, is targeted. Now, a person skilled in the art knows the negative impact of a high content of such charges on the erosivity of the powder containing it. Replacing at least part of the RDX with other energetic charges (such as EDNA), which are less erosive, is thus desirable. It would therefore be highly advantageous to have available a novel type of crosslinkable binder, which is crosslinkable with crosslinking agents that are not isocyanates.

In such a context, the inventors propose novel composite pyrotechnic products that are especially suitable as propellant powders for barrel weapons, containing a high content of charges in an energetic crosslinked binder. Said novel composite pyrotechnic products are optimized in terms of force (they contain a high content of energetic charges in an energetic binder), of vulnerability (they do not contain any nitrocellulose and may advantageously contain sparingly vulnerable energetic charges) and of production process (said process is easy to perform: without solvent, without precipitation for carrying out forming while the crosslinking begins, without pre-crosslinking) and they may also be optimized in terms of erosivity (they may advantageously contain EDNA charges in total or partial replacement for RDX charges).

According to its first subject, the present invention thus relates to novel composite pyrotechnic products. They are of the type comprising a crosslinked binder containing organic energetic charges (see above). Characteristically, their compositions, expressed as weight percentages, contain:

-   -   from 78% to 90%, advantageously from 80% to 86%, of organic         energetic charges, and     -   from 10% to 22% of an energetic crosslinked binder obtained by         crosslinking, via only 8% to 12% of its azide functions, a         polyglycidyl azide (PGA) with a number-average molecular weight         (Mn) of between 700 and 3000 g/mol, with at least one         crosslinking agent containing at least two propargyl functions         in its chemical formula, in the presence of a polymeric gum,         chosen from polyurethane-polyester gums, polyurethane-polyether         gums and mixtures thereof, the number-average molecular weight         of which is greater than 20 000 g/mol and the Mooney viscosity         of which is between 20 and 70 ML (5+4) at 100° C.; said         polymeric gum representing from 1% to 5% by weight of the         composition of said pyrotechnic product.

The composite pyrotechnic products of the invention thus contain a high content of organic energetic charges: from 78% to 90% by weight, advantageously from 80% to 86% by weight.

The charges under consideration (organic charges; mineral charges having been set aside insofar as they generate solid particles) are not per se original. They are organic energetic charges that are known per se and, for the most part, are already conditioned according to the prior art in a conventional organic polymeric binder (such as PBHT), especially crosslinked. The charges are advantageously hexogen (RDX), octogen (HMX), nitroguanidine (NGU), ethylene dinitramine (EDNA), N-guanylurea dinitramide (FOX 12 (GUDN)), 1,1-diamino-2,2-dinitroethylene (FOX 7 (DADE)), bis(triaminoguanidinium) 5,5′-azotetrazolate (TAGZT), dihydrazinium 5,5′-azotetrazolate (DHDZT), 5,5′-bis(tetrazolyl)hydrazine (HBT), bis(2,2-dinitropropyl)nitramine (BDNPN), a nitropyrazole, or a mixture of these energetic charges.

Within the composite pyrotechnic products of the invention there is thus a type of energetic charges, advantageously chosen from the above list, or a mixture of at least two types of energetic charges, advantageously chosen from the above list. EDNA organic energetic charges are preferably found therein. A mixture of EDNA charges and of RDX charges is particularly preferably found therein. It is in no way excluded to find only RDX charges or only EDNA charges, but, as indicated above, mixtures of EDNA charges and of RDX charges make it possible to achieve an optimum with reference to the force/erosivity compromise. It has been understood that the more said mixtures contain RDX, the more energetic they are, but the more erosive they are.

Energetic charges are in the form of solid grains homogeneously distributed in the crosslinked binder. These solid grains advantageously have, in a manner known per se, several particle size distributions.

We now come to the “key element” of the composition of the composite pyrotechnic products of the invention: the binder. This is present in a proportion of from 10% to 22% by weight, these 10% to 22% by weight including the 1% to 5% of gum.

It is a binder that is thermoset (crosslinked) in the presence of a gum, it is a binder which is obtained from a thermosetting (crosslinkable) polymer placed in contact with a gum. It is such an energetic binder, obtained from such an energetic polymer.

It is noted incidentally here that the term “a polymer” should be understood as meaning “at least one polymer” throughout the present text. Specifically, it is in no way excluded from the context of the invention for a mixture of at least two polymers (each of the type indicated and having different molecular weights and/or different degrees of branching) to be used.

The energetic polymer under consideration is a polyglycidyl azide (PGA).

It has a suitable molecular weight, number-average molecular weight (Mn) of between 700 and 3000 g/mol, advantageously between 1700 and 2300 g/mol, in reference to the consistency of its mixture, with essentially the charges and the gum (and to the mechanical properties desired for the is final product, which must be obtained with a low degree of crosslinking (see below)). Specifically, it must not be too liquid, so that a reasonable amount of gum suffices to thicken said mixture, which allows it to be formed (minimum mechanical strength and cohesion) before any crosslinking.

Said polymer is a polyazide, whence 1) its energetic properties and 2) its capacity to be crosslinked with crosslinking agents other than isocyanates.

Its crosslinking involves only 8% to 12% of its azide functions (such a low degree of crosslinking, performed on the polymer having the above molecular weight, allows the production of the final product with suitable mechanical properties). Said crosslinked polymer thus conserves its energetic properties. The binder for the composite pyrotechnic products of the invention is thus, as indicated above, an energetic binder. The force of said composite pyrotechnic products of the invention (containing a high content of energetic charges in a (crosslinked) energetic binder) is better understood.

As regards the nature of the energetic polymer and its crosslinking with crosslinking agents, other than isocyanates (such a crosslinking with isocyanates being possible via hydroxytelechelic functions when said polymer (PGA) is hydroxytelechelic) (see the technical problem of the use of charges with intrinsic acidity developed above), the inventors have, to their credit, made use of the concept of “Click chemistry”, more precisely of its application in the Huisgen cycloaddition reaction (1,3-dipolar cycloaddition) between an azide and an alkyne, said reaction giving a triazole. Said concept and its application mentioned above have been described in numerous publications, especially by Rostovtsev, Vsevolod V.; Green, Luke G.; Fokin Valery V. and Sharpless K. Barry in 2002 in Angewandte Chemie International Edition 41 (14), pages 2596-2599 (publication entitled: “A stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed Regioselective “Ligation” of Azides and Terminal Alkynes“). The crosslinked binder of the invention is thus obtained by crosslinking a prepolymer, as pointed out aboye, with at least one crosslinking agent containing alkyne functions, i.e. via triazole rings of formula:

More precisely, the at least one crosslinking agent used is a compound containing at least two propargyl functions in its chemical formula (”a polypropargyl“); it generally consists of a di- and/or tri-propargyl. Advantageously, it consists of dipropargyl succinate (DPS), dipropargyl maleate (DPM), tripropargyl tricarballylate (TCATP), the benzene ester of tripropargyl (BETP), and a dipropargyl poly(ethylene glycol) (PEG) with a number-average molecular weight of between 200 and 1500 g/mol. Very advantageously, it consists of dipropargyl succinate (DPS).

It is noted here that the compatibility of the organic energetic charges with the crosslinking agents of the type indicated has been checked (their placing in contact, “at high temperature” (70° C.), does not induce significant evolution of gas).

The composition of the composite pyrotechnic products of the invention also contains a polymeric gum (“crude rubber”) of the stated type. Said gum:

-   -   is chosen from polyurethane-polyester gums (i.e. of polyurethane         nature with flexible segments of polyester type),         polyurethane-polyether gums (i.e. of polyurethane nature with         flexible segments of polyether type) and mixtures thereof,     -   it has a number-average molecular weight of greater than 20000         g/mol (advantageously greater than 50000 g/mol, very         advantageously greater than 75000 g/mol), and     -   it has a Mooney viscosity of between 20 and 70 ML (5+4) at         100° C. This parameter is widely used in the rubber industry. “x         ML (5+4) at 100° C.” is understood as “x M=the viscosity in         Mooney units (or points); L or S (in this instance L)         corresponding to the size of the rotor, 5 indicating the         preheating time of the product and 4 is the time in minutes         after starting the motor at which the reading is taken, 100° C.         being the measuring temperature”. The value “x” is generally         given as “±y”; it is the value “x” which, according to the         invention, must be within the range 20-70 (limit values         included).

Such a gum is perfectly suitable for the purposes of the invention, insofar as it allows forming of the mixture to be crosslinked at a temperature below 100° C. (which is entirely compatible with the charges present), and does so without the use of solvent, without precipitation (for carrying out said forming while the crosslinking begins) and without any pre-crosslinking. Said gum is miscible with the polymer (PGA) (the gum/polymer mixture is “stable”, no exudation is observed). It exerts its (beneficial) action while being present in small amount (it represents a maximum of only 5% of the total weight of the product): its presence is therefore not detrimental in reference to the force of said products.

The inventors have, to their credit, identified (selected) this type of gum, which is perfectly suitable for the purposes of the invention.

Said gum generally consists of a polyurethane-polyester or a polyurethane-polyether gum, but mixtures of at least two gums (at least two polyurethane-polyester gums, at least two polyurethane-polyether gums or at least one polyurethane-polyester gum and at least one polyurethane-polyether gum; such mixtures of gums (gums within the meaning of the invention) constituting a gum within the meaning of the invention) having the required properties (recalled above) may be used. Said gum advantageously consists of a polyurethane-polyester gum.

This gum thus participates upstream of the crosslinking process, upstream of the forming step, as a manufacturing auxiliary. It is the gum which gives, without danger, to the charged polymer, by virtue of its properties (sufficient molecular weight and adequate viscosity), the required cohesion and mechanical strength. It is this gum which allows the easy preparation, without solvent, without precipitation (for carrying out forming while the crosslinking begins) and without pre-crosslinking, of the composite pyrotechnic products of the invention. It acts, at suitable temperatures (below 100° C.), as a thickener and cohesion agent for said charged polymer. By intervening upstream of any crosslinking, said gum, a manufacturing auxiliary, thus allows the easy manufacture of the composite pyrotechnic products of the invention. It is finally found interlaced in the crosslinked polymer (PGA) network.

It is noted, for all intents and purposes, that the crosslinked binder is thus the product resulting from the reaction, between the polymer (PGA) and the at least one crosslinking agent, performed in the presence of the gum and that it thus contains, besides said polymer crosslinked via triazole rings, said gum.

The composition of the composite pyrotechnic products of the invention is thus constituted essentially of the energetic charges and of the crosslinked binder (containing said gum). It may be constituted to 100% by weight of said energetic charges and of said crosslinked binder (containing said gum). It is generally thus constituted to at least 95% by weight, more generally to at least 98% by weight. In effect, it cannot be excluded for it to contain in addition at least one other additive; said gum, present in small amount, may quite rightly be considered as an additive: it is not an essential constituent of the binder, it is a manufacturing auxiliary whose intervention allows simple production of the desired product (according to the process described later in the present text). Such an at least one other additive, when it is present, is generally present in a proportion of from 0.1% to 5% by weight, more generally in a proportion of from 0.1% to 2% by weight. It may especially be at least one other additive, chosen from formulation agents (candelilla wax and/or paraffin wax), (energetic or non-energetic) plasticizers and stabilizers.

The composite pyrotechnic products of the invention, as described above, are entirely suitable as propellant powders for barrel weapons. Said composite pyrotechnic products of the invention thus consist advantageously of such powders. The composite pyrotechnic products of the invention, as described above, are also suitable, especially, as tactical propergol, explosive composition and gas generator.

The major advantage of the products of the invention becomes apparent from the foregoing text. The products are advantageous per se (in terms of force, vulnerability and wide field of application with reference to the nature of the charges) and insofar as they may be obtained via a process that is simple to perform (much easier to perform than the processes of the prior art).

Said process constitutes the second subject of the present invention. It comprises:

a) the provision of the ingredients below:

-   -   organic energetic charges,     -   a polyglycidyl azide (PGA) with a number-average molecular         weight (Mn) of between 700 and 3000 g/mol,     -   at least one agent for crosslinking said polyazide, containing         at least two propargyl functions in its chemical formula, and     -   a polymeric gum, chosen from polyurethane-polyester gums,         polyurethane-polyether gums and mixtures thereof, the         number-average molecular weight of which is greater than 20 000         g/mol and the Mooney viscosity of which is between 20 and 60 ML         (5+4) at 100° C.;

b) the production of a pasty mixture from said ingredients; the organic energetic charges, polyglycidyl azide and polymeric gum being used in suitable proportions relative to the desired composition of the final product, and said at least one crosslinking agent in the amount required for crosslinking from 8% to 12% of the azide functions of said polyglycidyl azide;

c) the production, from said pasty mixture, of at least one element in a desired form;

d) heat treatment of said at least one element for crosslinking of said polyglycidyl azide.

Said process thus comprises the provision of the (essential) constituent ingredients of the desired composite pyrotechnic products: the charges+the components, from which the crosslinked binder is obtained, i.e. the polymer, the at least one crosslinking agent and the gum. It has been indicated that the charges represent between 78% and 90% of the weight of the desired product, whereas the crosslinked binder represents between 10% and 22%, said 10% to 22% including the 1% to 5% of said gum (the remainder of said 1% to 5% corresponding to the product of reaction of the polymer and of the at least one crosslinking agent). Said at least one crosslinking agent is incorporated in an amount suitable for crosslinking the 8% to 12% of the azide functions of the polymer; it is generally incorporated to less than 5% by weight (more generally between 0.5% and 4%) of the reaction mixture. It is recalled here incidentally that additives, other than said gum, are liable to be incorporated.

With reference to each of the ingredients used for performing the process, reference may be made to the first part of the text relating to the product.

In a first stage, using the ingredients identified above, a pasty mixture is thus prepared, which is the precursor of the targeted final product (crosslinked). Such a pasty mixture is advantageously prepared with a twin-screw extruder (by extrusion) or with a two-roll mill, depending on the amounts to be used. It is generally prepared at a temperature of between 15° C. and 45° C. It may thus be prepared at room temperature or at a temperature above room temperature. In any case, incorporation of the gum allows said pasty mixture to be obtained, which can be manipulated and formed.

Starting with said pastry mixture, in the third step of the process of the invention, at least one element is prepared (n elements are thus generally prepared) in a desired form (directly that desired for the final product(s) or an “intermediate” form from which, after crosslinking (and generally chopping), said final product(s) having the desired form are obtained). Said third step is thus analyzed as a step of forming the paste. This forming may especially comprise spinning or calendering. After such spinning (performed in a press cylinder, having an outlet orifice of more or less substantial diameter), a spun product is obtained. This spun product is generally heat-treated for crosslinking and then chopped into strands (of the desired length). Such strands, which are suitable as propellant powders for barrel weapons, generally have a length of from 2 to 20 mm, for a diameter of from 1 to 20 mm (more generally for a diameter of from 2 to 15 mm). However, it is not excluded to chop the spun product (as strands which are thus not crosslinked) and then to crosslink said strands. On conclusion of such calendering, the calendered product, in the form of a plate (such a plate generally has a thickness of from 10 to 20 mm), may be chopped directly into platelets or heat-treated for crosslinking and then chopped into platelets.

According to implementation variants of the process of the invention, steps b and c of said process may comprise:

-   -   blending with a twin-screw extruder (or extrusion) and spinning,     -   blending with a two-roll mill and spinning, or     -   blending (with a twin-screw extruder or a two-roll mill) and         calendering.

The pasty mixture, formed into the desired form for the final product or into an intermediate form, is then heat-treated. The heat treatment must make it possible to ensure the expected result (crosslinking of the polymer) at a temperature that is not excessive (compatible with the presence of the energetic charges in a high content). Generally, said temperature is above 45° C. and remains below 80° C. Advantageously, the crosslinking is performed at 55° C. (±5° C.). Said at least one heat-treated element corresponds to the at least one desired product of the invention or makes it possible to obtain same, generally by chopping.

It is now proposed to illustrate the invention, in a manner that is not in any way limiting, in its product and process aspects, via the examples below.

1) Starting Materials Used

a) Commercial Products

-   -   Charges: RDX (0-100 CH; D₅₀=35 μm (D₅₀=diameter for which the         cumulative volume percentage is 50%)), sold by the company         Eurenco.     -   Binder: PGA, sold by the company Eurenco (Mn (number-average         molecular weight): 1900).     -   Gum: UREPAN® 643 G, sold by the company RheinChemie (product of         polyaddition of diphenylmethane diisocyanate and of a         polyester). It has the characteristics below:         -   number-average molecular weight: 80000 g/mol         -   Mooney viscosity: 40 (±10) ML (5+4) at 100° C.     -   Crosslinking agent: dipropargyl succinate, sold by the company         ARIAC.

b) Prepared Products

-   -   Charges: EDNA

The synthesis of ethylene dinitramine (EDNA) was performed in two stages via the isolation of an intermediate: dinitroethyleneurea (DNEU), in wet form, which was then transformed into EDNA.

Concentrated nitric acid was introduced into a jacketed 50 cm³ reactor. The nitrating bath was then cooled to a reaction temperature of 0° C. Once said bath reached 0° C., the introduction of imidazolidone was commenced. This reagent was introduced slowly so as not to exceed 20° C. The DNEU precipitated as soon as its concentration in the medium was greater than 23% by weight. The introduction of imidazolidone into the heterogeneous medium (nitrating bath+solid DNEU) was continued.

After the end of introduction of the imidazolidone, the medium was left stirring for 30 minutes at room temperature.

At the end of reaction, the mixture was poured into a bath of cold water at about 5° C. with stirring. The solid was then separated from the mother liquors by filtration, and washed several times with distilled water to neutral pH, then drained by suction. It was then taken up, in wet form, for the synthesis of EDNA.

The decarboxylation step was performed by addition of DNEU to a hot aqueous solution buffered with sodium acetate. Evolution of gas (of CO₂) was observed, which necessitated portionwise introduction of the powder.

Once the introduction of said DNEU powder was complete, the mixture was maintained at a stage of 95° C. to complete the formation of EDNA.

The reaction medium was then cooled to make the EDNA precipitate. The suspension was then filtered and then dried. A yield of 85% was obtained.

The production of EDNA was confirmed by infrared.

IR: 2936 cm⁻¹ aliphatic CH, 1593 cm⁻¹ NO₂, 1448 cm⁻¹ N=N, 1360 cm⁻¹ C—H.

The EDNA crystals obtained are coarse crystals (they have a D₅₀ of greater than or equal to 100 μm (D₅₀=diameter for which the cumulative volume percentage is 50%)). To use them, they are ground in a SWECO® mill. On conclusion of said grinding, they have a D₅₀ of 30 μm.

-   -   Crosslinking agent: propargyl polyethylene glycol with a         number-average molecular weight of 1000 g/mol (dipropargyl PEG         1000)

The synthesis was performed in accordance with the teaching of David Fournier, Richard Hoogenbooma and Ulrich S. Schubert in Chem. Soc. Rev., 2007, 36, 1369-1380 (“A straightforward approach to novel macromolecular architectures”).

PEG-1000 (50 g) was first introduced into a 100 mL three-necked flask; this flask was heated to a temperature of 45-50° C. to be able to be stirred. Next, sodium hydroxide at 40% by weight (6 g) was added, followed by dropwise addition of propargyl bromide, as a solution at 80% by weight in toluene (13.36 ml, 0.12 mol), with stirring. The medium was maintained at 65° C. for a period of 36 hours. At the end of reaction, 150 ml of dichloromethane were added to the reaction medium, cooled to room temperature. The resulting medium was then washed with water until a pH of the washing waters equal to 7 was obtained. The organic solution was then dried and the solvent was evaporated off.

The recovered product (35 g) was in the form of a wax.

Its identity was confirmed by ¹H NMR.

¹H NMR: 3.4 ppm (multiplet) C—H propargyl; 3.45 ppm (singlet) C—H₂ PEG; 4.18 ppm (doublet) C—H₂ propargyl

2) Process for Preparing Composite Pyrotechnic Products of the Invention

Composite pyrotechnic products of the invention of two types (Example 1 and Example 2) were prepared and tested. Their weight composition and their force (measured) are given, respectively, in Tables 1 and 2 below. Below each of said Tables 1 and 2, other characteristics of said products are indicated.

These composite pyrotechnic products of the invention were obtained from the starting materials identified above.

Step b of the process of the invention: the pasty mixtures were obtained in a two-roll mill, in a manner known per se. The gum was first introduced between the rollers of the two-roll mill (rolling mill), brought to a temperature of 38° C. It was thus softened. Next, a charges+PGA mixture (prepared beforehand in a container) was added. Candelilla wax (formulating agent) and then the crosslinking agent were then successively added to the resulting mixture (in a —C≡CH/—N₃ ratio equal to 10).

Step c of the process of the invention: the pasty mixtures obtained were introduced into a press cylinder heated to 38° C. to perform spinning at a pressure of between 180 and 220 bar.

Step d of the process of the invention: the heat treatment of the spun product was performed at 50° C. for 5 days. After chopping (of the crosslinked spun product), powder strands were obtained (diameter: 10 mm, length: 11 mm).

EXAMPLE 1

TABLE 1 weight % Binder URERAN ® 643 G 2.80 15.5 PGA 8.69 Dipropargyl PEG 1000 3.71 Candelilla wax 0.3 Charge RDX (0-100CH) 31.5 84.5 EDNA 53 100 F measured (MJ/kg) 1.2

Characteristics of the product obtained (after mixing with the two-roll mill, spinning and crosslinking) are indicated below.

Weight per unit volume: 1.619 g/cm³.

Mechanical properties at 20° C. in compression (10 mm/min):

Sm (maximum stress at break): 1.49 MPa

E (elastic modulus): 73.6 MPa

Em (maximum crush before break): 4%.

EXAMPLE 2

TABLE 2 weight % Binder UREPAN ® 643 G 3.43 15.3 PGA 10.55 Dipropargyl Succinate 1.02 Candelilla wax 0.3 Charge RDX (0-100CH) 31.2 84.7 EDNA 53.5 100 F measured (MJ/kg) 1.2

Characteristics of the product obtained (after mixing with the two-roll mill, spinning and crosslinking) are indicated below.

Weight per unit volume: 1.635 g/cm³.

Mechanical properties at 20° C. in compression (10 mm/min):

Sm (maximum stress at break): 11.8 MPa

E (elastic modulus): 184 MPa

Em (maximum crush before break): 13.6%. 

1. A composite pyrotechnic product containing organic energetic charges in a crosslinked binder, wherein a composition of said composite pyrotechnic product, expressed as weight percentages, contains: from 78% to 90% of organic energetic charges, and from 10% to 22% of an energetic crosslinked binder obtained by crosslinking, via only 8% to 12% of its azide functions, a polyglycidyl azide with a number-average molecular weight of between 700 and 3000 g/mol, with at least one crosslinking agent containing at least two propargyl functions in its chemical formula, in the presence of a polymeric gum, chosen from polyurethane-polyester gums, polyurethane-polyether gums and mixtures thereof, a number-average molecular weight of which is greater than 20000 g/mol and a Mooney viscosity of which is between 20 and 70 ML (5+4) at 100° C.; said at least one polymeric gum representing from 1% to 5% by weight of the composition of said pyrotechnic product.
 2. The composite pyrotechnic product as claimed in claim 1, wherein said organic energetic charges consist of hexogen, octogen, nitroguanidine, ethylene dinitramine, N-guanylurea dinitramide, 1,1-diamino-2,2-dinitroethylene, bis(triaminoguanidinium) 5,5′-azotetrazolate, dihydrazinium 5,5′-azotetrazolate, 5,5′-bis(tetrazolyl)hydrazine, bis(2,2-dinitropropyl)nitramine, a nitropyrazole, or a mixture of such charges.
 3. The composite pyrotechnic product as claimed in claim 1, wherein said organic energetic charges contain ethylene dinitramine charges.
 4. The composite pyrotechnic product as claimed claim 1, wherein said polyglycidyl azide has a number-average molecular weight of between 1700 and 2300 g/mol.
 5. The composite pyrotechnic product as claimed in claim 1, wherein said at least one crosslinking agent is selected from the group consisting in dipropargyl succinate, dipropargyl maleate, tripropargyl tricarballylate, the benzyl ester of tripropargyl, and a dipropargyl polyethylene glycol with a number-average molecular weight of between 200 and 1500 g/mol.
 6. The composite pyrotechnic product as claimed in claim 1, wherein said polymeric gum has a number-average molecular weight of greater than 50000 g/mol.
 7. The composite pyrotechnic product as claimed in claim 1, wherein said polymeric gum is a polyurethane-polyester gum or a polyurethane-polyether gum.
 8. The composite pyrotechnic product as claimed in claim 1, wherein the composition also contains from 0.1% to 5% by weight of at least one additive.
 9. The composite pyrotechnic product as claimed in claim 1, wherein the composite pyrotechnic product consists of a propellant powder for barrel weapons.
 10. A process for preparing at least one composite pyrotechnic product as claimed in claim 1, comprising: a) providing the ingredients below: organic energetic charges, a polyglycidyl azide (PGA) with a number-average molecular weight of between 700 and 3000 g/mol, at least one agent for crosslinking said polyazide, containing at least two propargyl functions in its chemical formula, and a polymeric gum, chosen from polyurethane-polyester gums, polyurethane-polyether gums and mixtures thereof, the a number-average molecular weight of which is greater than 20000 g/mol and the a Mooney viscosity of which is between 20 and 70 ML (5+4) at 100° C.; b) producing a pasty mixture from said ingredients; the organic energetic charges, polyglycidyl azide and polymeric gum being used in suitable proportions relative to the desired composition of the final product, and said at least one crosslinking agent in the amount required for crosslinking from 8% to 12% of the azide functions of said polyglycidyl azide; c) producing, from said pasty mixture, of at least one element in a desired form; and d) performing a heat treatment of said at least one element for crosslinking of said polyglycidyl azide.
 11. The process as claimed in claim 10, wherein said pasty mixture is prepared with a twin-screw extruder or a two-roll mill.
 12. The process as claimed in claim 10, wherein said pasty mixture is prepared at a temperature of between 15° C. and 45° C.
 13. The process as claimed in claim 10, wherein said at least one element is obtained by spinning or calendering.
 14. The process as claimed in claim 10, wherein said heat treatment is performed at a temperature above 45° C. and below 80° C.
 15. The composite pyrotechnic product as claimed in claim 1, wherein the composition, expressed as weight percentages, contains from 80% to 86% of organic energetic charges.
 16. The composite pyrotechnic product as claimed in claim 3, wherein said organic energetic charges contain hexogen charges and ethylene dinitramine charges.
 17. The composite pyrotechnic product as claimed in claim 6, wherein said polymeric gum has a number-average molecular weight of greater than 75000 g/mol.
 18. The composite pyrotechnic product as claimed in claim 7, wherein said polymeric gum is a polyurethane-polyester gum.
 19. The composite pyrotechnic product as claimed in claim 8, wherein said at least one additive is selected from formulation agents and plasticizers. 